Melt-processible Poly(tetrafluoroethylene)

ABSTRACT

Melt-processible, thermoplastic poly(tetrafluoroethylene) (PTFE) compositions are disclosed and methods for making and processing same. Additionally, products comprising these compositions are described.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional application60/095,583 filed Aug. 6, 1998 and priority from U.S. application Ser.No. 09/369,319 filed Aug. 6, 1999, the entire disclosure of both arehereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to melt-processible poly(tetrafluoroethylene)(PTFE), compositions thereof, articles formed therefrom, and methods formaking the same. More particularly, the present inventions relates to aparticular range of poly(tetrafluoroethylene) polymers which are readilymelt-processible while maintaining good mechanical properties. Further,the present invention relates to products made of melt-processible,thermoplastic PTFE compositions.

BACKGROUND OF THE INVENTION

Poly(tetrafluoroethylene) (PTFE) is well-known for, among otherproperties, its chemical resistance, high temperature stability,resistance against ultra-violet radiation, low friction coefficient andlow dielectric constant. As a result, it has found numerous applicationsin harsh physico-chemical environments and other demanding conditions.Equally well-known is the intractability of this important polymer.Numerous textbooks, research articles, product brochures and patentsstate that PTFE is intractable because, above its crystalline meltingtemperature, it does not form a fluid phase that is of a viscosity thatpermits standard melt-processing techniques commonly used for mostthermoplastic polymers (Modern Fluoropolymers, J. Scheirs, Ed. Wiley(New York), 1997; The Encyclopaedia of Advanced Materials, Vol. 2, D.Bloor et al. Eds., Pergamon (Oxford) 1994; WO 94/02547; WO 97/43102).Suitability of a polymer for standard melt-processing techniques may beevaluated, for example, through measurement of the melt-flow index (MFI)of the material (cf. ASTM D1238-88). Melt-processible polymers should,according to this widely employed method, exhibit at least a non-zerovalue of the melt-flow index, which is not the case for common PTFEunder testing conditions that are representative of, and comparable tothose encountered in standard polymer melt-processing. The extremelyhigh viscosity of PTFE, reported to be in the range of 10¹⁰-10¹³ Pa·s at380° C., is believed to be associated, among other things, with anultra-high molecular weight of the polymer, which has been estimated tobe in the regime well above 1,000,000 g/mol and often is quoted to be ofthe order of 10,000,000 g/mol. In fact, it is claimed (ModernFluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 240) that “toachieve mechanical strength and toughness, the molecular weight of PTFEis required to be in the range 10⁷-10⁸ g/mol . . . ”. Due to this highviscosity, common PTFE is processed into useful shapes and objects withtechniques that are dissimilar to standard melt-processing methods.Rods, sheets, membranes, fibers and coatings of PTFE are produced by,for example, ram-extrusion, pre-forming and sintering of compressedpowder, optionally followed by machining or skiving, paste-extrusion,high isostatic pressure processing, suspension spinning, and the like,and direct plasma polymerization.

Illustrative for the difficulties encountered in processing common PTFEare the complex and indirect methods by which fibers are produced fromthis polymer.

Polytetrafluoroethylene fibers have been produced, as described in U.S.Pat. No. 3,655,853, by forming a mixture of viscose and PTFE particlesin a dispersion, extruding the mixture through a spinneret into anacidic bath to form fibers consisting of a cellulosic matrix containingthe PTFE particles. After washing and rinsing, the fibers are heated toa temperature of about 70° C. to 390° C. to decompose the cellulosicmaterial and to melt and coalesce the polymer particles. The fibers arethen drawn at a ratio of about 4:1 to 35:1 typically at a temperaturebetween 370° C. and 390° C. The fibers produced by this relativelycomplex and expensive process may require further processing steps, suchas bleaching to remove residual contaminants, which commonly lowers thetensile strength. Another method to produce fibers of PTFE is describedin U.S. Pat. Nos. 3,953,566, 3,962,153, and 4,064,214. In this method apaste formed by mixing a lubricant, such as a mineral spirit, with afine powder of PTFE produced by coagulation of an aqueous dispersion ofPTFE particles, is extruded and formed to produce a tape, film or bead.The product thus formed, is slit to form fibers, is dried to remove thelubricant and subsequently stretched at a high rate, and at atemperature lower than the crystalline melt point of PTFE, to produce aporous article. The porous article is then heated while maintained inthe stretched condition to a temperature above the melt point ofcrystalline PTFE, generally considered to be in the range 327° C. to345° C., to increase strength. Alternatively, PTFE fibers are producedby first forming a solid preform by sintering the polymer for prolonguedperiods of time above the melting temperature of the polymer and coolingthe mass down to room temperature, which is a process that may take asmuch as 48 hrs. Subsequently, PTFE fibers are cut from the preform bythe well-know skiving method, typically yielding fibers of high denier(>>100).

Unfortunately, the above methods generally are less economical thancommon melt-processing, and, in addition, severely limit the types andcharacteristics of objects and products that can be manufactured withthis unique polymer. For example, common thermoplastic polymers, such aspolyethylene, isotactic polypropylene, nylons, poly(methylmethacrylate)polyesters, and the like, can readily be melt-processed into a varietyforms and products that are of complex shapes, and/or exhibit, forexample, some of the following characteristics: dense, void-free, thin,clear or translucent; i.e. properties that are not readily, if at all,associated with products fabricated from PTFE.

The above drawback of PTFE has been recognised virtually since itsinvention, and ever since, methods have been developed to circumvent theintractability of the polymer. For example, a variety of co-monomershave been introduced in the PTFE macromolecular chains that lead toco-polymers of reduced viscosity and melting temperature. Co-polymersare those that are polymerized with, for example, hexafluoropropylene,perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether),perfluoro(propyl vinyl ether), or perfluoro-(2,2-dimethyl-1,3-dioxole),partially-fluorinated monomers and combinations thereof, in addition tothe tetrafluoroethylene monomer. Several of the resulting co-polymers(for example, those referred to as FEP, MFA, PFA and Teflon® AF) provideimproved processibility, and can be processed with techniques for commonthermoplastic polymers (WO 98/58105). However, a penalty is paid interms of some or all of the outstanding properties of the homopolymerPTFE, such as reduced melting temperature and thermal and chemicalstability.

Additional methods to process the PTFE homopolymer include, for example,the addition of lubricants, plasticizers, and processing aids, as wellas oligomeric polyfluorinated substances and hydrocarbyl terminatedTFE-oligomers (for example, Vydax® 1000) (U.S. Pat. Nos. 4,360,488;4,385,026 and WO 94/02547). The latter method, however, is directed tothe improvement of the creep resistance of common PTFE which results ina bimodal morphology with two distinct melting temperatures, andgenerally does not lead to homogeneous PTFE compositions that can bemelt-processed according to standard methods. For example, only ahot-compression molding method is heretofore known for mixtures ofstandard PTFE and Vydax® 1000, that preferably is carried out in thenarrow temperature range between about 330° C. to 338° C. The otheraforementioned additions of lubricants, plasticizers, and processingaids also do not yield truly melt-processible PTFE compositions.Solution processing, at superautogeneous pressure, of PTFE fromperfluoroalkanes containing 2-20 carbon atoms has been disclosed in WO94/15998. The latter process is distinctly different frommelt-processing methods. Also disclosed is dispersion, and subsequentmelt-processing of standard PTFE into thermoplastic (host-) polymerssuch as polyetheretherketone and polyphenylene sulfide (WO 97/43102) andpolyacetal (DE 41 12 248 A1). The latter method compromises importantphysico-chemical properties of the resulting composition, when comparedto neat PTFE, or requires uneconomical and cumbersome removal of thehost material.

There exist PTFE grades of low molecular weight and of low viscosity.These grades, which are often are referred to as micropowders, commonlyare used as additives in inks, coatings and in thermoplastic and otherpolymers to impair, for example, nucleation, internal lubrication orother desirable properties that, in part, stem from the uniquephysico-chemical properties of the neat PTFE. Low molecular weight PTFEgrades, in their solid form, unfortunately, exhibit extreme brittlenessand, according to at least one of the suppliers, these PTFE grades . . .“are not to be used as molding or extrusion powders” (Du Pont, Zonyl®data sheets andurl:http://www.dupont.com/teflon/fluoroadditives/about.html—Jul. 7,1998).

Thus, a need continues to exist to develop melt-processible,thermoplastic poly(tetrafluoroethylene)s to exploit the outstandingproperties of this polymer in a wider spectrum of product forms, as wellas to enable more economical processing of this unique material.

SUMMARY OF THE INVENTION

Surprisingly, it has been found that poly(tetrafluoroethylene)s of aparticular set of physical characteristics provide a solution to theabove, unsatisfactory situation.

Accordingly, it is one objective of the present invention to providemelt-processible, thermoplastic PTFE compositions of good mechanicalproperties comprising PTFE grades that are characterized as having anon-zero melt-flow index in a particular range. As used herein, theindication “good mechanical properties” means the polymer has propertiessuitable for use in thermoplastic applications, and exhibits an strainat break of at least 10% or a stress at break of greater than 15 MPa,determined under standard ambient conditions at a strain rate of 100%per min.

Yet another object of the present invention is to providemelt-processible PTFE of good mechanical properties that exhibit aplateau value of the complex viscosity measured at frequencies belowabout 0.01 rad/s and at a temperature of 380° C. and strong shearthinning that is in a range beneficial for processing.

Still another object of the present invention is to providemelt-processible PTFE of good melt stretchability.

Another object of the present invention is to provide melt-processiblePTFE that in its oriented solid form has a crystallinity of betweenabout 1% and about 60% and good mechanical properties.

Still another object of the present invention is to provide amelt-blending method that yields melt-processible, thermoplastic PTFEcompositions of good mechanical properties comprising PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange.

Additionally, it is an object of the present invention to provide amethod to melt-process PTFE compositions that comprise PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange, into useful shapes and articles of good mechanical properties.

Still another object of the present invention is to provide usefulshapes and articles of good mechanical properties that are manufacturedby melt-processing of PTFE compositions that comprise PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange.

Yet another object of this invention is to provide novel useful shapesand articles that comprise PTFE.

Yet a further object of this invention is to provide a compositioncomprising tetrafluoroethylene polymer, or blend of two or moretetrafluoroethylene polymers wherein said polymer or said blend of twoor more polymers has a melt-flow index of between 0.2-200 g/10 min andis extensional or shear flow processible.

The present invention provides a melt-processible fluoropolymer having apeak melting temperature of at least 320° C. and good mechanicalproperties. And compositions and articles comprising at least in part acontinuous polymeric phase comprising a melt-processible fluoropolymerhaving a peak melting temperature of at least 320° C. and goodmechanical properties.

The present invention also provides a composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.And a process for producing a melt-processible composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.Also a method for producing an article comprising melt-processing acomposition comprising a melt-processible tetrafluoroethylene polymer,or a melt-processible blend of two or more tetrafluoroethylene polymerswherein said polymer or said blend of two or more polymers has goodmechanical properties.

Another aspect of the present inventions includes using themelt-processible polymer or polymer composition as an adhesive. Thepresent invention provides a process for connecting parts comprisingadhering a part to at least one further part with the polymer orcomposition of the present invention.

Additional objects, advantages and novel features of the presentinvention will be set forth in part in the description which follows,and in part will become apparent to those skilled in the art onexamination of the following, or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a stress-strain curve of a melt-processed film of PTFEaccording to the present invention.

FIG. 2 is a prior art commercial, sintered and skived film of common(ultra-high molecular weight) PTFE.

FIG. 3 is an optical micrograph (magnification 200×) of a thin sectionof PTFE according to the present invention into which 10% w/w of TiO₂was melt compounded

DETAILED DESCRIPTION OF THE INVENTION

The following is a list of defined terms used herein:

Void free—refers to a polymer or polymer composition, below itscrystallization temperature, having a void content lower than sinteredtetrafluoroethylene polymers including sintered tetrafluoroethylenepolymers modified up to 0.1 wt % with PPVE (which are reported to have avoid content of 2.6% or higher in the Modern Fluoropolymers, J. Scheirs,Ed. Wiley (New York 1997) at p. 253). Preferably, void free refers to apolymer or polymer composition, below its crystallization temperature,having a void content lower than 2% as determined by measuringgravimetrically the (apparent) density of a specimen and the intrinsicdensity via its IR spectroscopically determined amorphous content (asdiscussed in the Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York1997) at pp. 240-255, in particular p. 253; the entire disclosure ofwhich is, 1997, p. 240).

For the purpose of this invention, the ratio of the linear rate of fiberaccumulation V₂ (m/min) to the linear rate of melt-extrusion V₁ (m/min)at 380° C. is called the spin stretch factor (SSF). The stretching rateV_(st) (%/sec) is expressed by the following equation:

V _(st)=(V ₂ −V ₁)L×(100/60)

where L (m) is the distance between the orifice exit and solidificationpoint of the molten filament. The term (100/60) is for conversion to%/sec. The quantities SSF and V_(st) herein are used, among otherthings, to define melt-stretchability.

Monomeric units—refers to a portion of a polymer that corresponds to themonomer reactant used to form the polymer. For example, —CF₂CF₂—represents a monomeric unit derived from the monomer reactanttetrafluoroethylene.

The term PTFE grades as used herein refer to the fluoropolymer exclusiveof the fillers and/or other components. It is understood and well-knowthat added matter, such as fillers, reinforcing matter, dyes,plasticizers and the like, may influence various materialcharacteristics. The added matter, and the possible resulting effect onmaterials properties, however, are not to be considered in defining theparticular set of properties of the melt-processible PTFE of the presentinvention.

The Poly(Tetrafluoroethylene)s

The PTFE's according to the present invention generally are polymers oftetrafluoroethylene. Within the scope of the present invention it iscontemplated, however, that the PTFE may also comprise minor amounts ofone or more co-monomers such as hexafluoropropylene, perfluoro(methylvinyl ether), perfluoro(propyl vinyl ether),perfluoro-(2,2-dimethyl-1,3-dioxole), and the like, provided, howeverthat the latter do not significantly adversely affect the uniqueproperties, such as thermal and chemical stability of the PTFEhomopolymer. Preferably, the amount of such co-monomer does not exceedabout 3 mole percent (herein “mol %’), and more preferably less thanabout 1 mol %; particularly preferred is a co-monomer content of lessthan 0.5 mol %. In the case that the overall co-monomer content isgreater than 0.5 mol %, it is preferred that amount of the aperfluoro(alkyl vinylether) co-monomer is less than about 0.5 mol %.Suitable polymers include those having a peak melting temperature, asmeasured under standard conditions, that exceeds about 320° C.,preferably above 325° C. Preferably the polymer will have no peakmelting temperatures below 320° C. and more preferably the polymer willhave a single peak melting point which is above 320° C. Most preferredare PTFE homopolymers.

In addition, suitable poly(tetrafluoroethylene)s according to thepresent invention include those having good mechanical properties,combined with a highly beneficial thermoplastic flow behavior. Anindication of the thermoplastic flow behavior of the polymer can bereadily analyzed with the commonly employed method of the determinationof a melt-flow index (MFI). The latter method, for the present PTFE's isconveniently and reproducibly carried out according to ASTM testD1238-88, at 380° C. under a load of 21.6 kg, herein referred to as themelt flow index or alternatively MFI (380/21.6). Under theseexperimental conditions, and in a maximum extrudate-collection time of 1hr, conventional ultra-high molecular weight PTFE grades have an MFI ofzero.

Preferably, the PTFE grades according to the present invention have anon-zero MFI (380/21.6) in a maximum extrudate-collection time of 1 hr.More preferably, the PTFE's are characterized by an MFI (380/21.6) ofgreater than about 0.005, more preferably of greater than about 0.2 g/10min and most preferably of greater than 0.25 g/10 min. The maximum valueof the melt-flow index of the PTFE grades used in the present inventiondepends on the particular end product and processing technique. An uppervalue of the MFI of about 10 g/10 min is preferred for most applicationsin which the polymer solid is substantially isotropic; more preferred isan upper value of the MFI of about 5 g/10 min, and most preferred is 2.5g/10 min. As further elaborated upon below, the presence or absence ofmolecular orientation is readily established by heating the article to atemperature that is above its melting temperature. In embodiments inwhich the PTFE grades are employed in articles which are produced underprocessing conditions involving extensional or shear flow, and displayorientation of the polymer molecules as defined above, the PTFE gradesare characterized by a preferred range of the melt flow index of anupper limit of 200 g/10 min; more preferred the upper limit is about 75,and most preferred 50.

If in this case the PTFE grades according to the present inventioncomprise a relatively high content of comonomer the upper limit of theMFI range of the preferred grades could be higher. For example, if thePTFE contains up to 3 mol % of comonomer, the upper limit of the MFIrange could extend up to about 25 g/10 rain, and a preferred range wouldbe between 0.1 up to about 15; when the comonomer content is about 1 mol% or less, the MFI range may extend up to about 15 g/10 min, morepreferably the MFI range would be between 0.1 up to about 10 g/10 min;and at a content of 0.3 mol % or less the suitable MFI the preferredrange would not exceed about 5 g/10 min and more preferably would havean MFI value in the above-noted range for PTFE polymers. In the eventthe PTFE comprises a comonomer and is oriented even higher MFI indexcould be useful including MFI ranges up to about 300 g/min and morepreferably 250 g/min or less.

In another embodiment of the present invention, the PTFE grades areemployed in articles which are typically produced under processingconditions involving extensional or shear flow, such as melt-blown filmsand containers, fibers spun from the melt at a spin stretch factorgreater than 1, extrusion through conical dies, and the like. Generally,these processes result in articles that are not substantially isotropic,and display preferred orientation of the polymer molecules in one ormore directions. For example, in fibers spun under conditions involvingextensional flow, the polymer molecules typically elongate and orientinto the direction of the fiber axis. In melt-blown films, the polymermolecules commonly are elongated and oriented in the plane of the film.The presence or absence of preferred orientation of polymer molecules infinished articles, such as the above referred fibers and films, canreadily be established by heating the product to, for example, 10° C.above its melting temperature, at which point elongated and orientedpolymer molecules return to their relaxed isotropic state. The latterprocess results in macroscopic change of shape of the product. As anexample, a fiber, in which the polymer molecules are oriented along thefiber axis, will shrink along its long axis and increase in diameter,upon heating of that fiber to a temperature that is above its meltingtemperature. For the purpose of the present invention, articles are saidto be oriented when, upon heating to a temperature that is 10° C. aboveits melting temperature, after melting the article displays a change insize of at least 5% in at least one dimension. In embodiments in whichthe PTFE grades are employed in articles which are produced underprocessing conditions involving extensional or shear flow, and displayorientation of the polymer molecules as defined above, the PTFE gradesare characterized by a preferred range of the melt flow index of anupper limit of 200 g/10 min; more preferred the upper limit is about 75,and most preferred 50.

The highly beneficial thermoplastic flow behavior of thepoly(tetrafluoroethylene)s according to the present invention ischaracterized by their linear visco-elastic behavior, which isconveniently expressed as the absolute value of the complex viscosity.Preferably, the PTFE grades according to the present invention have a(Newtonean) plateau value of the complex viscosity measured atfrequencies below about 0.01 rad/s and at a temperature of 380° C. ofless than about 10⁹ Pa·s; preferably less than about 10⁸ Pa·s; and mostpreferred less than about 5.10⁷ Pa·s. The minimum plateau value of thecomplex viscosity of the PTFE grades according to the present inventiondepends on the particular end product and processing technique. Aplateau value of at least about 10⁶ Pa·s is preferred for mostapplications in which the polymer solid is substantially isotropic anddisplays no significant preferred orientation of the macromolecules.

In another embodiment of the present invention, the PTFE grades areemployed in articles which are typically produced under processingconditions involving extensional or shear flow, such as melt-blown filmsand containers, fibers spun from the melt at a spin stretch factorgreater than 1, extrusion through conical dies, and the like. In thisembodiment the PTFE grades are characterized by a preferred range of theplateau value of the complex viscosity of a lower limit of 10⁴ Pa·s ormore; more preferred the lower limit is about 2.10⁴ Pa·s, and mostpreferred about 5.10⁴ Pa·s. The PTFE grades according to the presentinvention additionally display a strongly reduced value of the complexviscosity measured at high frequencies. The latter property generally isindicative of strong shear thinning, which is highly beneficial for manymelt-processing operations, such as injection molding, melt-spinning,and the like. When measured at a frequency of 10² rad/s and at atemperature of 380° C., the preferred value of the complex viscosity islower than about 10⁵ Pa·s, more preferred below about 5.10⁴ Pa·s, andmost preferred below about 10⁴ Pa·s, but always more then about 10² Pas.

The PTFE grades of the present invention display an excellent meltstretchability, which is highly beneficial for, among other things,manufacturing of films, tapes, fibers, generally thin-walled structures,and the like. As understood herein, meltstretchability means the abilityof a melt of the polymer to be stretched without breaking at practicallyuseful rates. Thus, herein, a melt of the PTFE grades of goodmeltstretchability used in the present invention is defined as a melt,that is extruded at 380° C., that has a spin stretch factor (SSF) ofmore then about 1.1, and more preferred more then about 1.2, measured ata stretching rate of 10%/sec. Under the above conditions, common PTFEgrades cannot be extruded, and, thus, do not have a value of the spinstretch factor, as defined herein. Furthermore, unlike melts of commonPTFE grades, melts of the PTFE grades of the present invention can bestretched at surprisingly high rates without failure, for instance atrates greater than 10%/sec, preferably between 50 up to 5000%/sec, andmost preferably 100% sec up to 2500%/sec or more. Thesemeltstretchability characteristics are highly beneficial for, amongother things, high speed and economical manufacturing of films, tapes,fibers, generally thin-walled structures, and the like. As set forth inthe Examples, in one embodiment of the present invention PTFE melts arestretched at stretching rates of more then 10%/sec, more preferred atmore then 50%/sec, and most preferred at more then 100%/sec. Values ashigh as 1090%/sec have been achieved.

The poly(tetrafluoroethylene)s according to the present invention inaddition to having good mechanical properties, are characterized in arelatively low crystallinity, when in unoriented form, which isbeneficial for the toughness of products fabricated thereof. This degreeof crystallinity is conveniently determined by differential scanningcalorimetry (DSC) according to standard methods known to those skilledin the art of polymer analysis. Preferably, once-molten PTFE gradesaccording to the present invention that are recrystallized by coolingunder ambient pressure at a cooling rate of 10° C./min in unorientedform have a degree of crystallinity or between about 1% about 60% andpreferably between about 5% and about 60%, based on a value of 102.1 J/gfor 100% crystalline PTFE (Starkweather, H. W., Jr. et al., J. Polym.Sci., Polym. Phys. Ed., Vol. 20, 751 (1982)). When in the form ofproducts such as oriented fibers, tapes, films and the like, the PTFE'saccording to the present invention may exhibit values of thecrystallinity that are substantially higher than 60%, and may becharacterized by values as high as 95%, while maintaining goodmechanical properties.

Preferably, the PTFE grades according to the present invention arecharacterized by an MFI (380/21.6) between about 0.25 to about 200 g/10min and a degree of crystallinity of once-molten and recrystallizedunoriented material of between about 5% and about 60%. More preferably,the PTFE polymer is a polymer having a single peak melting pointtemperature which is above 325° C. and is preferably a homogenous blendof polymers and/or homopolymer.

The PTFE grades of the present invention can be synthesized according tostandard chemical methods for the polymerization of tetrafluoroethyleneas described in detail in the literature (for example, W. H. Tuminelloet al., Macromolecules, Vol. 21, pp. 2606-2610 (1988)) and as practicedin the art. Additionally, PTFE grades according to the present inventioncan be prepared by controlled degradation of common, high molecularweight PTFE or low co-monomer content copolymers thereof, for example bycontrolled thermal decomposition, electron beam, gamma- or otherradiation, and the like (Modern Fluoropolymers, J. Scheirs, Ed. Wiley(New York), 1997 the entire disclosure of which is hereby incorporatedby reference). Furthermore, and as demonstrated in the presentinvention, the PTFE grades according to the present invention can bemanufactured by blending of, for example, high melt-flow index gradeswith appropriate amounts of one or more grades of a lower, for instancebelow 0.5 g/10 min, or zero melt-flow index to yield homogeneouslyblended materials with values of the melt-flow index, viscosity orcrystallinity in the desired range. The latter, in effect bimodal,trimodal or blends of even higher modality, and generally, PTFE gradeswith a broad molecular weight distribution, are particularly beneficialfor use in processing schemes that involve elongation or shear flow,such as film blowing, melt-spinning of fibers at spin stretch factorsgreater than 1, extrusion through conical dies, and the like. Due to therelatively simple nature of the MFI-testing method, viscositymeasurement and crystallinity determination, using, for example, theseanalytical tools, those skilled in the art of polymer blending canreadily adjust the relative portions of the different PTFE grades toobtain the melt-processible, thermoplastic PTFE compositions accordingto the present invention. The present invention also contemplatescompositions and articles comprising a continuous phase having at least15 wt. %, preferably at least 45 wt. %, and more preferably at least 95wt % of the melt-processible tetrafluoroethylene polymer includingpolymers that are formed by blending two or more tetrafluoroethylenepolymers of the present invention. An exemplary composition couldinclude a composition or an article wherein the continuous phasecomposed of at least 99 wt. % of a PTFE homopolymer filled with a fillersuch as talc, glass and/or other inorganic or organic particles. It maybe that the filler comprise a between 10 to 90 wt. %, preferably between10 and 45 wt % and more preferably less than 30 wt. % of the totalcomposition (including continuous phase and filler).

The compositions according to the present invention optionally mayinclude other polymers, additives, agents, colorants, fillers (e.g.,reinforcement and/or for cost-reduction), property-enhancement purposesand the like, reinforcing matter, such as glass-, aramid-, carbon fibersand the like, plasticizers, lubricants, processing aids, blowing orfoaming agents, electrically conducting matter, other polymers,including poly(tetrafluoroethylene), fluorinated polymers andcopolymers, polyolefin polymers and copolymers, and rubbers andthermoplastic rubber blends, and the like. Depending on the particularapplication, one or more of the above optional additional ingredientsand their respective amounts are selected according to standardpractices known to those skilled in the art of standard polymerprocessing, compounding and applications.

Processing

The PTFE compositions according to the present invention can beprocessed into useful materials, neat or compounded, single- andmulti-component shapes and articles using common melt-processing methodsused for thermoplastic polymers that are well known in the art. Typicalexamples of such methods are granulation, pelletizing, (melt-)compounding, melt-blending, injection molding, transfer-molding,melt-blowing, melt-compression molding, melt-extrusion, melt-casting,melt-spinning, blow-molding, melt-coating, melt-adhesion, welding,melt-rotation molding, dip-blow-molding, melt-impregnation, extrusionblow-molding, melt-roll coating, embossing, vacuum forming,melt-coextrusion, foaming, calendering, rolling, and the like.

Melt-processing of the PTFE compositions according to the presentinvention, in its most general form, comprises heating the compositionto above the crystalline melting temperature of the PTFE's, which, ofonce-molten material, typically are in the range from about 320° C. toabout 335° C., although somewhat lower, and higher temperatures mayoccur, to yield a polymer fluid phase. Unlike standard (ultra-highmolecular weight) PTFE above its crystalline melting temperature, thePTFE grades according to the present invention form homogenous meltsthat can be freed from voids and memory of the initial polymer particlemorphology. The latter melt is shaped through common means into thedesired form, and, subsequently or simultaneously, cooled to atemperature below the crystalline melting temperature of the PTFE's,yielding an object or article of good and useful mechanical properties.In one preferred embodiment, shaped PTFE melts are rapidly quenched at acooling rate of more than 10° C./min, more preferably more than 50°C./min, to below the crystallization temperature to yield objects, suchas fibers and films, of higher toughness. In processing operationsinvolving transfer through one or more dies of melts of the PTFE such asin fiber spinning, film- and tape extrusion, and the like, in oneembodiment of the present invention it is highly beneficial to employconical dies of low entrance angle (less than 90°) as it is wellestablished that this reduces melt-instabilities and melt fracture, and,therewith, increases the processing speed.

In another embodiment of the present invention the PTFE is crosslinkedthrough, for example, irradiation and the like (Fuchs, B. and Scheler,U., Macromolecules 2000, vol. 33, p. 120). When crosslinked to yieldbranched materials, the latter may exhibit improved film-blowingcharacteristics, and if crosslinked to form macroscopic networks, thesematerials may be a rubber, or can be subsequently stretched in the meltto yield heat-shrinkable films, or may display increased resistance tocreep.

Certain articles, such as, but not limited to, fibers and films madeaccording to the present invention optionally may, subsequently, bedrawn or otherwise deformed in one or more directions, embossed, and thelike to further improve the physico-chemical, mechanical, barrier,optical and/or surface properties, or be otherwise post-treated (forinstance, quenched, heat treated, pressure treated, and/or chemicallytreated). The above methods and numerous modifications thereof and otherforming and shaping, and post-processing techniques are well know andcommonly practiced. Those skilled in the art of processing ofthermoplastic polymers are capable of selecting the appropriatemelt-processing and optional post-processing technology that is mosteconomical and appropriate for the desired end product, or productintermediate.

Products and Applications

The products contemplated according to the present invention arenumerous, and cover vastly different fields of applications. This isespecially true as PTFE has been approved also for food contact and forbiomedical applications. Without limiting the scope and use of thepresent invention, some illustrative products are indicated herein.Generally speaking, the products and materials according to the presentinvention include most or all applications that currently are covered bystandard (ultra-high molecular weight) PTFE, and many of its modified,melt-processible co-polymers. In many cases, the present products, whencompared with the latter, will have superior physical-chemicalproperties due to their predominant homopolymer character. Thus,applications are envisioned, among other industries, in the wire andcable industry, the printed-circuit board industry, semi-conductorindustry, the chemical processing industry, the semiconductor industry,the automotive industry, out-door products and coatings industry, thefood industry, the biomedical industry, and more generally in industriesand uses where any combination of high release, anti-stick,high-temperature stability, high chemical resistance, flame-resistance,anti-fouling, UV resistance, low friction, and low dielectric constantis required.

In particular, the PTFE may be used to form at least parts in articlessuch as, for example, is a wire (and/or wire coating), an optical fiber(and/or coating), a cable, a printed-circuit board, a semiconductor, anautomotive part, an outdoor product, a food, a biomedical intermediateor product, a composite material, a melt-spun mono- or multi-filamentfiber, an oriented or un-oriented fiber, a hollow, porous or densecomponent; a woven or nonwoven fabric, a filter, a membrane, a film, amulti-layer- and/or multicomponent film, a barrier film, a container, abag, a bottle, a rod, a liner, a vessel, a pipe, a pump, a valve, anO-ring, an expansion joint, a gasket, a heat exchanger, aninjection-molded article, a see-through article, a sealable packaging, aprofile, heat-shrinkable film, and/or a thermoplastically welded part.Preferred articles may include fibers, films, coatings and articlescomprising the same.

Typical examples of intermediate and end-user products that can be madeaccording to the present invention include, but are not limited togranulate, thermoplastic composites, melt-spun mono- and multi-filamentfibers, oriented and not, hollow, porous and dense, single- andmulti-component; fabrics, nonwovens, cloths, felts, filters, gas housefiltration bags; sheets, membranes, films (thin and thick, dense andporous); containers, bags, bottles, generally simple and complex parts,rods, tubes, profiles, linings and internal components for vessels,tanks, columns, pipes, fittings, pumps and valves; O-rings, seals,gaskets, heat exchangers, hoses, expansion joints, shrinkable tubes;coatings, such as protective coatings, electrostatic coatings, cable andwire coatings, optical fiber coatings, and the like. The above productsand articles may be comprised in part or in total PTFE compositionsaccording to the present invention, or optionally include dissimilarmaterials, such as for example in multi-layer and multi-component films,coatings, injection molded articles, containers, pipes, profiles, andthe like.

Due to the fact that the PTFE grades according to the present inventioncan be readily processed into mechanical coherent, tough, thin, denseand/or translucent objects, novel application areas for PTFE arecontemplated that heretofore were not readily or economically, if atall, accessible due to the intractability of standard (ultra-highmolecular weight) grades, notably in areas where the absence of remnantsof powder morphology and voids have prohibited use of the lattermaterial. Preferably, the polymer of the present invention hassufficient clarity such that if it were formed into a 1 mm thick film,and tested at a temperature below its crystallization temperature, itwould be sufficiently translucent to enable images viewed through thefilm to be readily recognized, preferably without distortion.

Exemplary applications of the polymer and polymer composition of thepresent which take advantage of some of these beneficial propertiesinclude see-through, sealable and/or heat-shrinkable packaging, barrierfilms and caps, conformal coatings, dense tubing and linings,thin-walled and complex injection-molded parts, and the like.

The PTFE grades according to the present invention, due to theirthermoplastic nature, not only are useful for the simple and economicproduction of finished goods and intermediate products, but also forother functions. An illustrative example of such function, withoutlimiting the scope of the present invention, is adhesion and welding.The latter is a well-recognized difficulty associated with common PTFE(Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 251).The PTFE grades according to the present invention were found to beoutstanding adhesives, for example, for itself as well as for otherfluoropolymers, preferably including common high-molecular weight PTFEproducts such as films, sheets and the like. Simply by inserting a smallamount of a PTFE grade according to the present invention in powder,film or other form between two or more surfaces that one desires toadhere together, liquefying the former material, and subsequentlysolidifying under slight or modest pressure, it was found to yield avery strong adhesive bond that was provided by the inventive PTFEgrades.

EXAMPLES

The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. It isunderstood that the examples are given by way of illustration and arenot intended to limit the specification or the claims that follow in anymanner.

General Methods and Materials

Melt-Flow Index. Values of the melt flow index (MFI) as discussed hereinare determined in accordance with the ASTM Standard D1238-88 at atemperature of 380° C. and under a load of 21.6 kg during a maximumextrudate-collection time of 1 hr using a Zwick 4106 instrument.

Viscosity. The absolute values of the complex viscosities of differentPTFE grades were measured from small amplitude oscillatory shearexperiments (Rheometrics Dynamic Spectrometer RDS-II) at 380° C. forseveral frequencies between 100 rad/s and 3.10⁻³ rad/s using standardplate-plate geometry. The linear range was estimated from strain-sweepexperiments at 100 rad/s.

Thermal Analysis. Thermal analysis was conducted with a Netzschdifferential scanning calorimeter (DSC, model 200). Samples of about 5mg were heated at a standard rate of 10° C./min. Unless indicatedotherwise, melting temperatures given herein refer to the endotherm peaktemperatures of once molten (at 380° C.) and cooled (at 10° C./min)material. Crystallinities were determined from the enthalpies of fusionof the same specimen taking the value of 102.1 J/g for 100% crystallinePTFE (Starkweather, H. W., Jr. et al., J. Polym. Sci., Polym. Phys. Ed.,Vol. 20, 751 (1982)). Mechanical Data Tensile tests were carried outwith an Intron Tensile Tester (model 4411) at room temperature ondumbbell-shaped specimen of 1-2 mm gauge length and 2 mm width andfibers. The gauge fiber length was 20 mm. The standard strain rate was100%/min.

Materials. Various grades of PTFE, purchased from Du Pont (Teflon®,Zonyl®), Ausimont (Algoflon®) and Dyneon, were used. The following TableI presents an overview of the melting temperatures and thecrystallinities of materials that were once molten at 380° C. andrecrystallized by cooling at 10° C./min, and MFI (380/21.6) of thedifferent grades, which include grades both outside the invention, andthose according to the present invention.

TABLE I Melting MFI PTFE Temperature* Crystallinity (380/21.6) grade (°C.) (%) (g/10 min) I Zonyl ® MP 1200 325.9 64.8 >>1,000 II Zonyl ® MP1100 325.0 67.2 >1,000 III Zonyl ® MP 1600N 329.0 68.9 150 IV Dyneon ®9207 329.8 65.1 55 V Zonyl ® MP 1000 329.3 59.5 52 VI blend V/XX** 331.660.5 35 VII Dyneon ® 9201 330.5 60.9 22 VIII blend V/XX** 331.4 59.9 15IX Zonyl ® MP 1300 329.9 60.5 10 X Algoflon ® 330.7 61.7 9 F5A EX XIZonyl ® MP 1400 330.8 57.3 2.8 XII Algoflon ® L206 332.3 60.8 2.6 XIIIblend IX/XX** 331.2 51.9 1.8 XIV blend XI/XIX** 329.3 49.9 1.2 XV blendV/XIX** 329.4 51.4 1.0 XVI blend XI/XIX** 329.7 47.6 0.8 XVII blendIX/XX** 330.5 50.9 0.8 XVIII blend IX/XX** 331.5 47.5 0.6 XIX Zonyl ® MP1500J 327.5 44.2 0.2 XX Teflon ® 6 328.6 33.7 0.0 XXI Dyneon TFM ® 327.027.0 0.0 1700 *Note: all grades exhibited the well-know thermaltransitions around room temperature, typical of PTFE, and only one mainmelting endotherm at the elevated temperatures above indicated. **forcompositions and preparation of blends see Examples 7 and 9.

Comparative Example A

PTFE grades I-XII (Table I) were melt-compression molded at 380° C. witha Carver press (model M, 25 T) for 5 min at 1 metric ton (t), 10 min at10 t, and then cooled to room temperature during 4 min under 4 t intoplaques of about 4×4×0.1 cm. All grades were found to yield brittleproducts (strain at break of less then 10%) most of which could not beremoved from the mold without fracture.

Example 1

Example A was repeated with PTFE grades XIII-XVIII. The materials weremelt-compression molded at 380° C. with a Carver press (model M, 25 T)for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled to roomtemperature during 4 min under 4 t into plaques of about 4×4×0.1 cm.These grades were found to yield mechanically coherent, and translucentsamples that could readily be removed from the mold and bend withoutfracture. Mechanical testing of the plaques indicated that the strain atbreak of all samples exceeded 10%; typical values exceeded 250%.

Comparative Example B

Attempts were made to melt-compression mold at 380° C. with a Carverpress (model M, 25 T) films of PTFE grades I-XII. All grades were foundto yield brittle products that could not be mechanically removed fromthe mold without fracture.

Example 2

Example B was repeated with PTFE grades XIII-XVIII. The materials weremelt-compression molded at 380° C. with a Carver press (model M, 25 T)for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled to roomtemperature during 4 min under 4 t into thin films of about 15×15× about0.025 cm. These grades were found to yield mechanically coherent,translucent and flexible films that could readily be removed from themold.

The mechanical properties of the melt-processed PTFE films were measuredaccording to the standard method detailed above. A typical stress-straincurve is presented in FIG. 1 (A), for comparison purposes, together withthat of a sample of commercial, pre-formed/sintered and skived film of0.40 mm thickness (B). This figure shows that the melt-processed PTFEfilm (here of grade XVI (Table I)) has the typical deformationproperties of a thermoplastic, semi-crystalline polymer with a distinctyield point and strain hardening. The stress-strain curves A and Bresemble each other, which indicates that these melt-processed PTFEfilms do not have substantially inferior mechanical properties whencompared to common, PTFE of ultra-high molecular weight. The mechanicaldata of the two products are collected in Table II.

TABLE II Yield Strain at Stress Tensile Strength Break PTFE film (MPa)(Nominal, MPa) (%) Skived Film 12.8 36.1 476 Melt-processed Film of 12.620.9 427 PTFE grade XVI

The excellent mechanical properties of the film according to the presentinvention were not affected by storing the sample for periods in excessof 15 hrs at temperatures of 200° C. and higher and had a strain andstress at break that were within experimental error identical to therespective values of the non-heated films.

In addition, we observed that the melt-processed PTFE films, unlike thecommercial skived material, were dense and translucent, through whichtext readily could be read up to a film thickness of about 1 mm.

Comparative Example C

PTFE grades I-V, VII, IX-XII and XX were introduced into a laboratorymelt-spinning apparatus (SpinLine, DACA Instruments), the temperature ofwhich was kept at 380° C., and that was equipped with a die of 1 mmdiameter (length/diameter ratio 1, entrance angle 45°). PTFE grades I-V,VII, IX-XII could not be collected as monofilaments due to brittlenessof the extrudate, leading to premature fracture. Ultra-high molecularweight PTFE grade XX could not be melt-spun, even at loads up to 5 kN(limit of equipment), due to the high viscosity (zero MFI) of thematerial.

Example 3

Example C was repeated with PTFE grade XV. PTFE monofilaments werecollected without draw down (spin stretch factor substantially equalto 1) onto bobbins. The filaments were tough, and could readily be drawnat room temperature to draw ratios exceeding 4 (strain at break largerthen 300%).

The mechanical properties of the melt-spun fibers were measuredaccording to the method detailed above. Their tensile strength was 0.11GPa.

Comparative Example D

PTFE grades I-V, VII, IX-XII and XX were introduced into a laboratory,recycling twin-screw extruder (MicroCompounder, DACA Instruments), thetemperature of which was kept at 380° C., and that was equipped with anexit die (entrance angle 90°) of 2 mm diameter. PTFE grades I-V, VII,IX-XII could not be collected as continuous extrudates due to extremebrittleness of the extrudate, leading to premature fracture. Ultra-highmolecular weight PTFE grade XX could not be extruded due to the highviscosity (zero MFI) of the material.

Example 4

Example D was repeated with PTFE grades XIII-XVIII. Continuous PTFEextrudates were readily collected without draw down (spin stretch factorsubstantially equal to 1). The extrudates could readily be chopped intogranulate or drawn into monofilaments.

Example 5

PTFE grade XV was melt-compounded at 380° C. in a Brabender DSK25segmented, co-rotating extruder (25 mm diameter; 22 aspect ratio) with0.1 weight % of various dyes (Amaplast® Blue HB, Red RP, Yellow NX,Color Chem. Int. Corp.), 10% of TiO₂ (Fluka), 10 weight % of aramid pulp(Twaron®, Akzo Nobel), and 20 weight % of chopped, 15 mm long carbonfiber, respectively. Subsequently, the compounded materials obtainedwere melt-processed into plaques according to the method in Example 1.Optical microscopy on thin sections (about 0.1 mm) revealed that in allcases extremely homogeneous mixtures and composites were obtained (FIG.3) without significant aggregation of the added matter. This exampleshows that PTFE according to the present invention can bemelt-compounded.

Comparative Example E

Two strips of about 7×1×0.04 cm of commercial, skived film of highmolecular weight PTFE were pressed together in a Carver press (model M,25T) at a temperature of 380° C. under a load of less than 1 t for 2 minand subsequently cooled to room temperature. Without much force, thestrips could be separated from each other, which is indicative of pooradhesion, and illustrates the difficulties encountered in welding ofcommon PTFE.

Example 6

Comparative Example E was repeated. However, a small piece ofmelt-processed film of PTFE grade XV (about 1×1×0.02 cm) was placed inbetween the two strips of about 7×1×0.04 cm of commercial, skived filmof high molecular weight PTFE. This sandwich structure was also pressedtogether in a Carver press (model M, 25T) at a temperature of 380° C.under a load of less than 1 t for 2 min and, subsequently, cooled toroom temperature. The strips could be separated from each other onlyafter one or both of the skived material strips exhibited excessiveplastic deformation, which is indicative of outstanding adhesiveproperties of this grade to, for example, common PTFE.

Example 7

Various amounts (total quantity 90 g) of PTFE grades V and XXI, XI andXXI, V and XIX, XI and XIX, and IX and XX, respectively, (see Table 1)were introduced into a Brabender melt-kneader (model Plasti-corder PL2000), which was kept at a temperature of about 380° C., 60 rpm. Afterabout 1 min, a clear homogeneous melt was formed that behaved like amelt of ordinary thermoplastics. Mixing was continued for 10 min, afterwhich the blended product was discharged. The MFI values of thedifferent blends were measured. The results are given in Table III.

TABLE III Weight Ratio MFI (380/21.6) PTFE grades (—) (g/10 min) XI +XXI 60-40 0.4 IX + XX 45-55 0.6 IX + XX 50-50 0.8 V + XXI 60-40 0.8 XI +XIX 10-90 0.8 V + XIX 12.5-87.5 1.0 XI + XIX 25-75 1.2 IX + XX 60-40 1.8This example shows that PTFE grades according to the present inventionof an MFI value in a desired range can be prepared by melt-blending ofPTFE grades of substantially different MFI.

The same PTFE samples were processed into films according to the methodin Example 2. All films were found to exhibit good mechanical properties(strain at break >10%).

Example 8

Various amounts (total quantity 90 g) of PTFE grades V and XIX, and IXand XX, respectively, (see Table 1) were introduced into a Brabendermelt-kneader (model Plasti-corder PL 2000), which was kept at atemperature of about 380° C., 60 rpm. After about 1 min, a clearhomogeneous melt was formed that behaved like a melt of ordinarythermoplastics. Mixing was continued for 10 min, after which the blendedproduct was discharged. The absolute values of the complex viscositiesof various PTFE samples were measured from small amplitude oscillatoryshear experiments. The results are given in Table IV.

TABLE IV Weight Ratio Viscosity PTFE grades (—) (Pa · s) V + XIX 60-409.3 · 10⁵ V + XIX 40-60 5.5 · 10⁶ V + XIX 20-80 8.4 · 10⁶ V + XIX 10-901.3 · 10⁷ IX + XX 60-40 1.2 · 10⁷ IX + XX 50-50 1.8 · 10⁷ IX + XX 45-552.4 · 10⁷The same PTFE samples were processed into films according to the methodin Example 2. All films were found to exhibit good mechanical properties(strain at break >10%).

Example 9

In order to produce relatively high MFI (>2.5 g/10 min) PTFE grades of abroad molecular weight distribution, various amounts (total quantityabout 5 g) of grades I, V, IX and XI with, respectively, grades XX andXXI (see Table 1) were introduced into a laboratory, recyclingtwin-screw extruder (MicroCompounder, DACA Instruments, Santa Barbara,Calif.), the temperature of which was kept at 380° C., and that wasequipped with an exit die (entrance angle 90°) of 2 mm diameter. After10 min of mixing at a rate of 50 rpm, the rate was reduced to 10 rpm,and the blended products were extruded at a linear rate of 15 cm/minthrough the orifice. The MFI values of the different blends weremeasured. The results are given in Table V.

TABLE V Weight Ratio MFI (380/21.6) PTFE grades (—) (g/10 min) I + XXI 90-10 180 I + IX + XXI 45-45-10 23 V + XX 98-2 35 V + XX 95-5 20 V + XX 90-10 15 V + XXI 98-2 31 V + XXI 95-5 19 V + XXI 92.5-7.5 13 V + XXI 90-10 9 IX + XXI 95-5 7The above blended PTFE grades were introduced into a laboratorymelt-spinning apparatus (SpinLine, DACA Instruments), the temperature ofwhich was kept at 380° C., and that was equipped with a die of 0.5 mm or1.5 mm diameter (length/diameter ratio 1, entrance angle 45°). Themolten polymers typically were extruded at rates of about 0.1-7.0 m/min,although higher rates were possible and no upper limit was detected. Theliquid filaments were cooled and solidified typically in water at adistance of 1 cm below the orifice, although cooling in air alsoproduced satisfactory results. All blends could readily be collected inthe form of continuous fibers at spin stretch factors (SSF) of about 1.2to more than 4 and at stretching rates V_(st) as high as 1000%/sec andmore. With the above process, PTFE fibers were produced with diametersof a wide range from 0.5 mm to 80 μm and lower, which translated inapproximately 3500 to 90 denier. It is contemplated that use of dies oflower diameter and/or higher spin stretch factors will result in theformation of PTFE fibers of diameters as low as 10 μm or less.The mechanical properties of the various as-spun fibers were testedaccording to the method described above. Examples of measured fiberproperties are collected in Table VI below.

TABLE VI Stretch Stress at Strain at PTFE grades/ SSF Rate DiameterBreak Break Weight Ratio (—) (—) (%/sec) mm (MPa) (%) V + XX/98-2 40.8764 0.23 17 6 V + XX/95-5 12.1 214 0.27 20 8 V + XX/90-10 7.8 131 0.4524 12 IX + XXI/95-5 1.9 160 0.30 30 15 IX + XXI/95-5 2.9 1090 0.20 26 6V + XXI/95-5 30.4 564 0.15 79 7 V + XXI/95-5 4.8 660 0.20 52 10 V +XXI/95-5 1.3 347 0.19 35 14 V + XXI/92.5-7.5 1.2 280 0.30 54 16 V +XXI/90-10 21.7 397 0.15 91 10 V + XXI/90-10 1.3 347 0.29 79 18 I +XXI/90-10 2.0 160 0.25 36 12 I + IX + XXI/ 3.9 987 0.08 201 8 45-45-10In order to further increase the mechanical properties of these fibers,they may be subsequently stretched according to methods well-know tothose skilled in the art. By employing multi-orifice devices it iscontemplated that multi-filament yarns can be produced according to theabove methods. Also, it is contemplated that through the use of PTFEcompounded with, for example, colorants, microscopic whiskers ofreinforcing matter, and/or conductive particles, multi-functional PTFEfibers can be obtained according to the present invention.

The melting temperature of the above fibers were determined using thestandard DSC method, and were found to be in the range of 328° C. to333° C. In order to determine whether or not the fibers were oriented, asection of 30 cm was cut from each of the fibers and heated in an hotoven to a temperature that was 10° C. above their respective meltingtemperatures. All fibers displayed shrinkage, (original length−finallength)/original length×100%, along the fiber axis of more then 5%.Typical values were in the range from about 80%-95%, with higher valuesgenerally found for fibers of a higher spin stretch factor.

These examples illustrate that also relatively high melt-flow-index(>2.5 g/min) PTFE grades of broad molecular weight distributions, suchas bimodal trimodal and the like, according to the present inventionunder conditions of flow leading to oriented products can be processedinto products of good mechanical properties.

Example 10

An amount of 1 gram of a PTFE composition of 10% w/w of PTFE grade XXIand 90% w/w of grade I prepared as in Example C, and placed between twometal surfaces that were kept at a temperature of 380° C. Once thepolymer was molten, the metal surfaces were separated to a distance of30 cm from one another at a rate of about 10 cm/sec; a thin film of PTFEwas obtained. The latter, semi-transparent film had a thickness of 12μm, and excellent mechanical properties (tensile strength of more than15 MPa). This example demonstrates that according to the presentinvention PTFE can be processed into thin films, which may be ofparticularly beneficial use in the semi-conducting industry and inpackaging. It is contemplated that such process can also be carried outwith film extrusion and blowing.

Having described specific embodiments of the present invention, it willbe understood that many modifications thereof will readily appear or maybe suggested to those skilled in the art, and it is intended thereforethat this invention is limited only by the spirit and scope of thefollowing claims.

1-67. (canceled)
 68. A melt-processable fluoropolymer, the fluoropolymerbeing a copolymer of tetrafluoroethylene and one or more comonomers;said one or more co-monomers being present in less than 1 mol %; thefluoropolymer having a crystalline melting temperature of about 320° C.;a stress at break of greater than 15 MPa (at room temperature and astrain rate of 100% min); a crystallinity in the range of 5 to 60%(based on a value of 102.1 J/g for 100% crystalline PTFE); and amelt-flow index (according to ASTM D 1238-88 at 380° C. under a 21.6 kgload) of greater than 0.25 g/10 min, and less than 75 g/10 min.
 69. Thefluoropolymer of claim 68, wherein said fluoropolymer has no peakmelting temperature below 320° C.
 70. The fluoropolymer of claim 68,wherein said comonomer consists essentially of perfluoroalkylvinylether.
 71. The fluoropolymer of claim 70, wherein saidperfluoroalkylvinyl ether is perfluoropropylvinyl ether.
 72. Thefluoropolymer of claim 68, wherein said one or more comonomers arepresent in less than 0.5 mol %.
 73. The fluoropolymer of claim 68,wherein a 1 mm thick film of the fluoropolymer is translucent, at atemperature below its crystallization temperature.